Abstract Tobacco use remains the leading cause of preventable death in the United States. Smoking is increasingly a disease of medically underserved populations, including individuals of lower socioeconomic status and those with behavioral or substance use disorders. Emergency departments (EDs), to which Americans paid 130 million visits in 2013, are excellent clinical settings in which to identify smokers, initiate treatment, and refer for aftercare. Our previous work has demonstrated the efficacy of a multicomponent intervention in promoting tobacco abstinence at 3 months. The intervention included a full package of evidence-based treatments, including initiation of nicotine replacement therapy in the ED, provision of 6 weeks of patches and gum, a brief motivational interview, active referral to a state smokers' quitline, and a brochure with information on the health risks of smoking. A subsequent pilot study demonstrated the feasibility and potential efficacy of an intervention that included short-message-service (SMS) texting to subject cellphones to promote tobacco abstinence. While efficacious, it is not clear which components of the intervention had the greatest impact, which combinations of therapy might work best, or which are generalizable to all EDs. In order to design an intervention that is clinically effective, cost-effective, and practicable, we propose to disentangle the effects of these components and assemble an intervention that maximizes clinical efficacy, feasibility, and acceptability, given a cost- effectiveness constraint and findings from qualitative analysis. The methodology we propose using is the Multiple Optimization Strategy (MOST), a clinical trials design that uses principles adapted from industrial engineering. We propose an innovative 16-arm full-factorial design in a cohort of 1056 adult smokers in an urban ED, to test the efficacy of four key components: motivational interviewing, initiation of nicotine replacement medication, quitline referral, and texting. All subjects will receive a smoking cessation brochure. At the trial's completion, we will use a novel mixed-methods approach to identify components that were efficacious within the proposed cost constraint, along with feasibility and acceptability to subjects. We will assemble components found to be clinically efficacious, cost-effective, and feasible/acceptable into a multicomponent package for testing in a future randomized clinical trial. Study Aim (1) is to conduct the factorial experiment; Aim (2) is to analyze trial results to identify the effective components, and Aim (3) is to lay the groundwork for the subsequent clinical trial testing this multicomponent intervention, versus a control condition. The multicomponent intervention, once disseminated and implemented, can transform the care of the tens of millions of smokers who visit U.S. EDs. Our team includes an outstanding array of experts with deep experience in trial design, including the developer of MOST, emergency department-based investigation, tobacco dependence treatment, texting, health economics, and qualitative methods.